School Notes: School of the Environment
May/June 2008

Study offers new paradigm on ecosystem ecology

Predators have considerably more influence than plants over how an ecosystem functions, according to a study that was published in February in Science. The findings, according to the author, Oswald Schmitz, Oastler Professor of Population and Community Ecology at the environment school, are a "revolutionary" shift in thinking on the subject. Ecosystem ecologists have long held that plants and their interaction with the soil determine the type and abundance of herbivores and carnivores in an ecosystem. Schmitz's paper, "Effects of Predator Hunting Mode on Grassland Ecosystem Function," shows that the opposite is true.

"Most ecosystem ecologists think that the supply of nutrients in plants determines who can live up in higher trophic (feeding) levels," said Schmitz. "This study shows that it's the top trophic levels determining how the plants interact with the soil."

In the three-year-long experiment, conducted at the Yale-Myers Forest, scientists observed different spiders hunting prey and noted the effects of that activity on the surrounding ecosystems. "What's really cool here is that different spiders have different hunting modes, and it's those modes that cause grasshoppers to behave differently, which then carries down the chains of the community structure of the plants," said Schmitz. Spiders that searched for prey, instead of lying in wait, induced the grasshoppers to shelter in -- and eat -- the dominant plant species, promoting plant diversity. Added Schmitz, "Plants, ecosystem ecologists say, have an indirect effect on carnivores. My research shows that carnivores have an indirect effect on plants." Funding for the study was provided by the National Science Foundation's ecological biology program.

Website calculates economic impact of emissions reduction

A national policy to cut carbon emissions by as much as 40 percent over the next 20 years could still result in increased economic growth, according to an interactive website reviewing 25 of the leading economic models being used to predict the economic impacts of reducing emissions.

Robert Repetto, professor in the practice of economics and sustainable development and creator of the site, said, "As Congress prepares to debate new legislation to address the threat of climate change, opponents claim that the costs of adopting the leading proposals would be ruinous to the U.S. economy. The world's leading economists who have studied the issue say that's wrong. And you can find out for yourself."

The interactive website, www.climate.yale.edu/seeforyourself, synthesized thousands of policy analyses in order to identify the seven key assumptions accounting for most of the differences in the models' predictions. The site allows visitors to choose which assumptions they feel are most realistic and then view the predictions of the economic models on the basis of the chosen assumptions. "The website shows that even under the most unfavorable assumptions regarding costs, the U.S. economy is predicted to continue growing robustly as carbon emissions are reduced," said Repetto. "Under favorable assumptions, the economy would grow more rapidly if emissions are reduced through national policy measures than if they are allowed to increase as in the past."